Abstract Detail

Chromosome number in Solanum sejunctum: The potential role of polyploidy in the origin of an Australian dioecious species.

The living collection of Solanum sejunctum currently growing in the greenhouse at SUNY Plattsburgh is the first ever and only cultivated population of this species. In an attempt to better understand the evolution and natural history of breeding systems in the genus Solanum, we are conducting research on the pollination biology and origin of divergence between S. sejunctum and its sister species, S. asymmetriphyllum. Solanum sejunctum is a particularly interesting species to study as it is recently described and, although it was assumed to be dioecious, tests have not been done to confirm this. In all confirmed cases within Solanum, dioecy is functional; female flowers bear pollen, but that pollen is without germinal apertures (inaperturate). Solanum sejunctum is geographically limited to a single sandstone outlier off the Arnhem Plateau known as Mt. Brockman, on the eastern edge of Kakadu National Park (Northern Territory). The two species mentioned above are the only dioecious Solanum species found within the Kakadu region and have been shown by phylogenetic analysis to share a single common ancestor. One way two species can diverge in sympatry is through a polyploid event. Symon (1981) considers polyploidy a likely generator of diversity in Australian “spiny” solanums (Solanum subgenus Leptostemonum), making such a hypothesis plausible for Solanum sejunctum. Ploidy in S. sejunctum was confirmed using traditional chromosome counts as well as a ploidy analyzer.